In order to improve the wearability of some mechanical parts, such as gear, piston and cylinder, a wear-resistant coating is commonly arranged on the surface of these parts. During long-term service of these parts, however, the naturally occurring grown-in micro-defects thereof still will accumulate slowly, and may interact with post micro-damages, so that fatal damage will occur since quantitative change finally leads to qualitative change. If one definite signal can be obtained before the damage of the parts due to qualitative change appears, or the process of quantitative change accumulation for micro-damages of parts can be precisely mastered, accidents can be avoided as much as possible.
At present, fatigue wear tests on part surface mostly take variation of the factors such as vibration, frictional coefficient, and temperature as a judging basis for evaluating abrasion state of part surfaces. When the actual value of the selected judging factors exceeds a pre-determined threshold value, it indicates failure of the part surface. Afterwards, the failed part is subjected to fracture analysis to reversely infer the mechanism of failure by experience or classical theory. However, such failure behavior and mechanism study mainly characterized by “ex-post judgment” cannot estimate critical failure state of the part surfaces. Hence, a controlling mechanism capable of dynamically monitoring and controlling failure of part surface is impossible to be established.
At present, on-line monitoring of the damage on the part surface mainly relies on the piezoelectric sensor arranged for collecting information on the working status of the parts, so that the variation in the service state of the surface coating can be monitored by sorting and analyzing the signal exported from the sensor. Among these, the piezoelectric sensor is prepared according to the piezoelectric effect of existing piezoelectric materials such as barium titanate and lead titanate, which is required to be disposed around the coating in service or bonded to the mechanical equipments or parts during application.
However, there are problems, such as weak strength or distortion of the damage information on the surface coating of the part, when the prior art piezoelectric sensors are used to dynamically monitor the damage situations of the coating in service on the part surface.